1,4-DIETHYNYLBENZENE BRIDGED FE(CP(ASTERISK))(DPPE) UNITS - MIXED-VALENCE 35-ELECTRON AND BISIRON(III) 34-ELECTRON COMPLEXES

Reaction of the bis(alkyne) HC=CC6H4C=CH with 2 equiv of [Fe(eta(5)C(5)Me(5))(eta(2)dppe)Cl] (1) [dppe = ethylenebis(diphenylphosphine)] and NH4PF6 in methanol produces the vinylidene complex [{Fe(eta(5)C(5)Me(5))(eta(2)dppe)}(2)-mu-(C=CHC6H4CH=C)][PF6](2) (2), isolated as a brown powder in 83% yield. This complex is readily deprotonated by 2 equiv of KOBu(t) in THF and yields the alkynyl derivative [{Fe(eta(5)C(5)Me(5))(eta(2)dppe)}(2)-mu-(C=CC6H4C=C)] (3) as a thermally stable orange solid in 96% yield. The addition of 2 equiv of [{Fe(eta(5)C(5)Me(5))(2)][PF6] to a CH2Cl2 solution of 3 gave the Fe(III)-Fe(III) complex 5, isolated as a dark green microcrystalline solid in 90% yield that is air and thermally stable. The paramagnetic salt 5 was characterized by IR in the solid state, and in solution, by Mossbauer and ESR spectroscopies, and magnetic susceptibility measurements. The CV shows two reversible redox systems with quite a large wave separation (\Delta E(0)\ = 0.26 V) corresponding to a large comproportionation constant (K-c = 2.6 x 10(4)). The mixed-valence complex [{Fe(eta(5)C(5)Me(5))(eta(2)dppe)}(2)-mu-(C=CC6H4C=C)][PF6] (4) was prepared and isolated in 95% yield by addition of a stoichiometric amount of [Fe(C5H5)(2)][PF6] to a suspension of 3 in CH2Cl2. As shown in Mossbauer, ESR, and IR spectroscopies, the rigid binuclear assembly allows the odd-electron delocalization on the two metal centers over an 11.89-Angstrom span.